Figure 8.

N-myc renders PNCs insensitive to hedgehog antagonists. (A,B) PNCs were infected with either GFP or N-myc encoding viruses for 24 h, and then cultured for an additional 24 h in the absence or presence of 3 μM cyclopamine prior to transplantation into the cerebellum of SCID-beige mice. Tumors developed in all animals transplanted with N-myc infected cells, whether or not they had been exposed to cyclopamine. (A,B) Sections of a tumor derived from N-myc-infected PNCs pretreated with cyclopamine, stained with DAPI (A) to label all nuclei or with antibodies against N-myc (green) and Ki67 (red) to detect proliferating tumor cells (B). Magnification, 20×. (C) Tumor cells from ptc^+/− mice were cultured in the absence or presence of 1 μM cyclopamine or 25 ng/mL bFGF for 48 h, and then pulsed with ³H-Td for an additional 18 h before being assayed for ³H-Td incorporation. (D) Tumors resulting from transplantation of N-myc infected PNCs were harvested and FACS-sorted to purify infected (GFP⁺) cells. These cells were cultured in the absence or presence of 1 μM cyclopamine or 25 ng/mL bFGF and analyzed as described above. Cyclopamine and bFGF markedly inhibited the growth of ptc^+/− tumor cells but only modestly inhibited the growth of tumors derived from N-myc-infected PNCs (data in C and D are representative of five and three replicates, respectively).